This invention relates to the art of removal of aflatoxin from cereals, oil seeds and feedstuffs which are contaminated therewith and, more particularly, to an improved method for the removal of aflatoxin from cereals, oil seeds and feedstuffs.
It is of course well known that aflatoxin is a specific mycotoxin produced by the action of a fungi belonging to the genus, aspergillus, on grain, seeds, kernels or nuts. Aflatoxins are a group of related, complex, hetercyclic chemical compounds. These compounds are very slightly soluble in water and in the crystalline form melt (and decompose) at temperatures in the 240.degree. C. to 280.degree. C. range.
Aflatoxin contamination is particularly problematic in the peanut industry and, in addition, can affect grains such as corn and rice, other oil seeds such as cotton seed, and meals of such grains and seeds which are often used as feed for domestic animals. The growth of fungi which produce aflatoxin is favored under the same conditions which are good for growing nuts and grains. High levels of aflatoxin in foods and feeds presents a threat to humans and animals in that aflatoxins have been shown to cause cancer in laboratory animals. Accordingly, the U.S. Food & Drug Administration has set limits on the amount of aflatoxin that can be in food products, namely less than 20 ppb. The production of aflatoxin results from unfavorable conditions of harvesting and storage, namely high humidity and moisture content.
Peanuts often contain visibly damaged kernels which often contain high contents of aflatoxins. The darker color of these kernels, especially after roasting, enables them to be sorted out thus reducing aflatoxin content. However, it is well known that the mold mycelia can enter perfectly sound peanuts producing aflatoxins in kernels that show no visible imperfections. Thus, even the most rigorous color sorting will often fail to reduce the aflatoxin of highly contaminated lots of peanuts to acceptable levels.
A wide variety of processes have been explored heretofore with respect to reducing the level of aflatoxin contamination in peanuts and peanut meal, including autoclaving, heat treating or roasting, chemical inactivation and microwave heating at atmospheric pressure. All of these processes have met with some success, insofar as reduction of aflatoxin is concerned, but there are limitations and disadvantages which accompany these processes and which either result in less than desired reductions in the level of aflatoxin contamination, result in a contaminated product which is not commercially acceptable and/or involve process parameters which are not acceptable in connection with the production of product on a commercial basis. For example, normal peanut roasting, either oil or dry, to produce a commercially acceptable peanut, such acceptance basically being by color, only reduces aflatoxin B1 by about 5% to 40%. In many cases, this reduction is due to the fact that roasting has excessively darkened damaged kernels to the point where they can be color sorted. In any event, if the contamination level is 200 ppb, for example, roasting leaves the contamination level unacceptably high. While aflatoxin B1 can be reduced by about 80% by roasting at high temperatures and/or for long periods of time, the latter results in the peanuts being over roasted and unacceptable either because of the excess browning color thereof and/or the loss of the nutritional value thereof.
Other efforts to reduce aflatoxin contamination have included chemical inactivation through the use of ammonia, methylamine, sodium hydroxide, ozone and acetone, for example. Chemical treatment or extraction, however, is undesirable for a number of reasons including process time, the provision and cost of special equipment, and the potential for residual odor in the decontaminated product. Peanuts and peanut meal have also been microwave roasted at atmospheric pressure as an alternative to conventional oven roasting. Those familiar with the application of microwave energy will understand that it is a penetrative radiation. When peanuts or other objects are subjected to microwaves, the heating effect is from the center out. This is contrasted to conventional oven methods where hot gases are used to heat or roast the peanuts by convection. In turn the interior of the kernel is heated by conduction. Experience has shown that microwave roasting produces a very uniform product in shorter times. As with conventional roasting aflatoxin content is reduces. However, to reduce the aflatoxin content to an acceptable level often results in over roasting and thus browning and/or nutritional loss.
Peanuts roasted conventionally require a 30 to 40 minute heating cycle and temperatures of 125.degree. to 150.degree. C. (260.degree. F. to 300.degree. F.) depending on the color desired. Usually, the peanuts have been pre-dried and are normally supplied for roasting containing 7% to 8% moisture. The first part of the cycle thus involves drying. As the material approaches 1%-2% moisture the various color and flavor reactions take place. At the same time, various oils, chemical constituents, and particles are either steam distilled, sublimed, or entrained and exit with the exhaust air.